Obesity Clinical Trial
Official title:
Effect of High-flow vs. Low-flow Nasal Oxygenation on Spontaneous Ventilation in Obese Adult Patients During Analgo-sedation for Vitrectomy, Randomized Controlled Trial
Patients suffering from pathology of posterior eye chamber such as diabetic retinopathy,
retinal detachment, traumatic eye injury, retained lens fragments, macular hole, pucker,
dislocated intraocular lens after cataract surgery or vitreomacular traction are often
subjected to pars plana vitrectomy (PPV). PPV is minimally invasive endo-microscopic
operation usually performed in topical anesthesia combined with sub-Tenon or retrobulbar
block done by surgeon, supplemented by intravenous analgo-sedation given by anesthesiologist.
Continuous infusion and dose adjustment of intravenous anesthetics applied should procure
moderate sedation and preservation of patients' spontaneous ventilation. However, despite
carefully applied anesthetics and standard low-flow nasal oxygenation (LFNO) (5 L/min O2 via
nasal catheter), inadequate spontaneous breathing can occur leading to low blood oxygen level
(hypoxia). Obese patients are susceptible to hypoxia and hypercapnia (high CO2 blood level)
during analgo-sedation. Respiratory instability of obese patients is often associated to
their subsequent circulatory instability (heart rate and blood pressure disorders).
On the other hand, high-flow nasal oxygenation (HFNO) is usually used during anesthesia
induction when difficult maintenance of airway patency is expected, in intensive care units
during weaning patients from mechanical respirator and in postanesthesia care units during
awakening from anesthesia. It can deliver 20 to 70 L/min, up to 100% inspiratory fraction of
O2 (FiO2) to patient. High oxygen/air flow produces 3-7 cmH2O of continuous pressure in
patients' upper airways therefore providing better oxygenation. Oxygen/air mixture delivered
by HFNO is humidified and heated, thus more comfortable to patient than dry and cold LFNO.
Aim of this study is to compare effect of HFNO to LFNO during intravenously applied
standardized analgo-sedation given for PPV in obese adult patients.
Investigators hypothesize that obese patients, whose breathing pattern is preserved,
receiving HFNO vs. LFNO during standardized analgo-sedation for PPV will be more respiratory
and circulatory stable, preserving normal blood O2 and CO2 level, breathing pattern, heart
rate and blood pressure.
Patients suffering from pathology of posterior eye chamber such as diabetic retinopathy,
retinal detachment, traumatic eye injury, retained lens fragments, macular hole, pucker,
dislocated intraocular lens after cataract surgery or vitreomacular traction are often
subjected to pars plana vitrectomy (PPV).
PPV is minimally invasive micro-endoscopic surgery of posterior eye chamber. Patients usually
receive analgo-sedation combined with topical anesthesia, which, depending on the type of
surgery, precedes a regional, retrobulbar or sub-Tenon block. Although lower doses of
intravenous anesthetics are carefully titrated in continuous infusion and standard, low -
flow nasal oxygenation (LFNO) is applied, patients are prone to respiratory insufficiency.
Obese patients are especially susceptible to bradypnoea, transitory apnoea, hypoxia and
hypercapnia. Respiratory instability is then often followed by circulatory one presented by
heart rate and blood pressure deflections from baseline values. It is known that higher
anesthesia risk obese patients may suffer from serious complications due to respiratory
issues during analgo-sedation, even fatal outcome may occur.
LFNO is applied at rate of 5 L/min O2 per nasal catheter, reaching inspiratory fraction of
oxygen (FiO2) of 40%. High-flow nasal oxygenation (HFNO) is an innovative method of patient
oxygenation that delivers warmed and moistened oxygen and air mixture with a flow rate of up
to 70 L/min and up to 100% FiO2 via specially designed soft nasal cannula. It is known that
40 L/min of oxygen/air mixture delivered by HFNO provides 40% FiO2 applying continuous
positive inspiratory pressure of 3-7 cmH2O which ensures continuous non-invasive support of
patients' spontaneous ventilation and thus better oxygenation stability of the patient.
OBJECTIVE: The study aims to determine the effect of HFNO versus LFNO on the stability of
spontaneous ventilation during standardized intravenous analgo-sedation for PPV in normal
weight and obese patients.
HYPOTHESIS: Investigators hypothesize that administration of HFNO in comparison with LFNO in
patients with preserved spontaneous breathing during the standard analgo-sedation procedure
will contribute to better oxygenation maintenance and, consequently, greater peri-procedural
safety of patients, especially in obese patients.
Investigators expect that HFNO will provide reduced bradypnoea intervals (bradypnoea <12
breaths/min, FoB 1/min), longer maintenance of adequate oxygenation, shorter intervals of
desaturation (peripheral blood oxygen saturation - SpO2≤92%), reducing hypercapnia
(expiratory carbon-dioxide - expCO2≥45 mmHg) and less airway opening maneuvers performed by
attending anesthesiologist (AOM). These will prevent partial respiratory insufficiency
detected by low SpO2 accompanied by low or normal expiratory carbon-dioxide level (expCO2),
and global respiratory insufficiency detected by decreased SpO2≤92% and increased expCO2≥45
mmHg.
Investigators plan to conduct prospective, parallel group, randomized controlled clinical
trial. Trial will be managed according to principles of Declaration of Helsinki for
scientific clinical research and will be planned and guided according to CONSORT guidelines
(Consolidated Standards of Reporting Trials). The trial has been approved by Hospital's Ethic
Committee.
The source of information are going to be 126 adult patients scheduled for PPV under
analgo-sedation. Eligible participants will be interviewed and examined ambulatory by
anesthesiologist, their ASA status, difficulty of airway management and body mass index (BMI)
evaluated. After initial examination inclusive and exclusive criteria will be distinguished.
Eligible participants who give voluntarily their written consent of participation will be
included in this study. After that, participants will be assigned to equal normal weight
(18<BMI<30 kg/m2), class I obesity (30≤BMI<35 kg/m2) and class ≥II obesity (BMI≥35 kg/m2)
groups. Each group will be randomized to intervention (HFNO) and control (LFNO) subgroup by
computer random numbers generator. Randomization will be used until adequate number of
participants in every subgroup is reached.
Interventions: intervention subgroups participants will be oxygenated via nasal cannula using
high flow (40 L/min) of humidified and heated oxygen in air mixture (FiO2 40%). HFNO will be
applied by oxygenator (AirVO™2, Fisher and Paykell, New Zealand, Technomedika, Croatia
d.o.o.) during procedural analgo-sedation for PPV maintaining spontaneous breathing. In
control subgroups, LFNO will be applied via nasal catheter (Bauerfeind d.o.o. Zagreb,
Croatia) using standard low-flow oxygen (5 L/min, FiO2 40%). In both groups concentration of
oxygen delivered depends on oxygen flow which is regulated by standard flow-regulator
(flowmeter). Oxygen is delivered through pipelines from central hospital gas supply or from
portable cylinder gas supply.
Anesthesia procedure will be uniformed for all participants. Integrated noninvasive
monitoring of circulatory function (heart rate - EKG, intermittent mean arterial pressure -
sphygmomanometer) will be set (Compact 7; Medical Econet GmbH, Germany). Respiratory vital
functions: oxygenation (pulse oximeter), heart rate and expCO2 by using capnometer
(Capnostream™35 Portable Respiratory Monitor, Medtronic, Belgium).
Every participant will have established intravenous infusion of 250 ml NaCl 0.9% via
intravenous cannula regulated by continuous flow (Extension set/CONTROL-A-FLO Regulator 19
"Male Luer Lock Adapter", Baxter/Agmar d.o.o. United States of America/ Croatia).
Oxygenation (HFNO or LFNO) will be continuously administered before institution of
analgo-sedation until patients' awakening. It will be started 3 minutes before
analgo-sedation (preoxygenation), continued during analgo-sedation and procedure of PPV
(perioperative oxygenation) and up to 5 minutes after PPV and until patient is awake
(postprocedural oxygenation).
Induction of analgo-sedation will be instituted by droperidol 1.25 -2.5 mg bolus accompanied
by continuous infusion of target remifentanyl concentration up to 0.05 mcg/kg/min. Intensity
of sedation will be measured by Ramsay's sedation scale (RSS). Moderate sedation (RSS 4) is
characterized by: purposeful response to verbal or tactile stimulation, no intervention
required for airway patency maintenance, adequate spontaneous ventilation and sufficient
cardiovascular function. Surgeon will apply topical local anesthetic on conjunctiva which is
followed by regional anesthesia (sub-Tenon or retrobulbar block). Intravenous analgo-sedation
will be administered via perfusor (B.Braun, Melsungen, Germany). Analgo-sedation will be
discontinued immediately after end of PPV.
Control of nasopharyngeal airway is achieved by using oropharyngeal airway, if necessary.
Oropharyngeal airway (Airway; Vigon-Medicpro d.o.o.) will be inserted after achieving
moderate analgo-sedation and only if base of tongue is closing airway by dropping on
posterior pharyngeal wall. Every manipulation of patients airway by anesthesiologist will be
documented (insertion of airway, jaw thrust maneuver).
Measuring:
SpO2, expCO2, heart rate (fC) and respiratory rate (fD) will be measured continuously, and
simultaneously continuously noted in 5 minutes intervals - T0=before oxygenation, T1=15
minutes after instituting LFNO or HFNO after beginning of analgo-sedation, T2=when patient is
awake after oxygenation ends.
Noninvasive measurement SpO2 will be performed by indirect method using a pulse oximeter on
the index finger of the left hand (Compact 7, Medical ECONET GmbH, Germany).
Blood pressure measuring and mean arterial pressure calculation will be repeated
intermittently in 5 minutes intervals prior to-, during analgo-sedation and after patient is
awaken. All measured parameters will be noted in identical intervals.
The data will be collected uniformly by three researchers: an anesthesiologist who interviews
and examines patients ambulatory, an anesthesiologist designated for procedural
analgo-sedation and an anesthesiologist who will collect the data after the completion of the
analgo-sedation procedure.
The investigator in charge of the data collection will collect it from the pre-operative
ambulatory list and the anesthesiologist list. The anesthesiology sheet will include all data
from the trend table of the monitored vital parameters and from the simultaneously noted
respiratory rate (fD) per minute and the expCO2.
The data will be collected through non-invasive measurements: peripheral blood oxygen
saturation (SpO2), heart rate (fC), respiratory rate (fD), blood pressure (mean arterial
pressure - MAP), carbon dioxide exhaled values before, in the stabilization and at the end of
the analgo-sedation, i.e. 5 minutes after awakening of the patient.
A fourth researcher will be in charge of entering the collected data into the database. The
statistician will analyze the data.
Basic data analyses will be performed by statistician. Sample size is determined by statistic
computing web program: http://www.stat.ubc.ca/~rollin/stats/ssize used statistic test
Inference for Proportions:Comparing Two Independent Samples. Assessment of sample size is
computed for two independent samples with assumption of clinically significant difference in
patients' oxygenation: ≤88 and ≥99%. Statistical significance of difference will be inferred
with 5% α-error, 50% β-error and study power 0.80.calculated size of sample is: 21
participant pro subgroup (total of 126 participants).
Possible biases and confounding variables could be caused by hypothermia of the participant
and by sphygmomanometer pressure on the same arm where peripheral oxygenation level is
measured. These difficulties can be bypassed by: adjustment of room temperature where
analgo-sedation for PPV is performed and blood pressure measuring cuff placed on right arm
(pulse oximeter placed on left index-finger).
Any possible event that may occur during analgo-sedation that causes deviation from the study
protocol will be the reason for exclusion of the subjects from the study and the PPV will be
continued under anesthesia according to the rules of good clinical practice.
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